High Efficiency and Reduced Emissions Boiler System for Steam, Heat, and Processing
Dr. Guido Poncia | United Technologies Research Center
Objectives of the Demonstration
The objective of this project was to demonstrate a cost-effective solution to the problem of improving boiler efficiency and reducing emissions by means of a novel combustion control system and a sensor package. A new combustion control and monitoring system was brought from Technology Readiness Level (TRL) 4 to TRL6, and its effectiveness was demonstrated in a retrofit of the 30-year-old Trane 25 one million British thermal units (MMBtu) dual fuel boiler (natural gas and No. 2 oil) at Watervliet Arsenal (WVA) in New York state. The demonstration occurred in three phases, aimed at assessing efficiency performance with the legacy mechanical system, the commercially available state-of-the-art (SoA) oxygen (O2) trim solution, and the new carbon monoxide (CO)/O2 trim solution. In this way, a comparison among technologies and benefits associated with adoption of the proposed solution could be precisely quantified.
The demonstrated control solution was intended for retrofit of hot water or steam generation boilers with capacities larger than 10 MMBtu/hr. The technology included continuous monitoring of flue gas concentrations of O2 and CO to improve the boiler fuel-to-steam efficiency by means of regulation of the burner inlet fuel valve and air damper. The boiler efficiency control system incorporated a novel control algorithm, low-cost sensors to monitor exhaust composition, and a user-friendly tool for visualization of boiler performance. The controller continuously maintained the optimum proportion of fuel and air feeding the burner in order to reduce inefficiencies arising from excess air content while preventing unsafe operation arising from incomplete combustion. This new system was an evolution of a commercially available O2 trim solution developed on the Fireye PPC4000 product platform and contrasts with legacy systems with preset mechanical linkage by using electronic driven servomechanisms to set the ratio of fuel to air.
During a one-year testing campaign between February 2011 and March 2012, it was demonstrated that the new system would enable fuel savings of 4% for typical utilization with natural gas and an equivalent reduction of carbon dioxide (CO2) emissions. Stated performance objectives (5% fuel costs savings) were not met for the demonstration boiler when fired with natural gas. Nevertheless, the investment in the new technology on a similar boiler burning natural gas would pay back in slightly more than 2 years with expected fuel savings of $17,000 yearly. Although the new system was not tested with No. 2 oil, it was demonstrated that 7% fuel savings are achievable with a SoA efficiency control product on which the new technology is based.
Boiler performance of all configurations was assessed in terms of combustion efficiency, fuel-to-steam efficiency, and emission levels, and compared with preset performance objectives. As performance is dependent on the specific operating point of the boiler, the evaluation was performed at different steady state conditions corresponding to levels of steam output and corresponding firing rates. The following was observed for operation with natural gas:
- Combustion efficiency improved with the adoption of O2 trim technology by 1% to 2% across the firing range. An additional improvement of 0.5% to 1% was observed by introducing CO/O2 trim at an operation range below 60% of maximum fuel utilization. Measured performance did not meet originally stated objectives (more than 6% improvement over baseline).
- The improvements above had an impact on overall fuel-to-steam efficiency, with improvements of 2% to 3% with the introduction of O2 trim over baseline and an additional 0.5% to 1% with CO/O2 trim for operating ranges below 60% of fuel utilization. Measured performance did not meet originally stated objectives (more than 5% improvement over baseline).
- Throughout the demonstration, CO and nitrogen oxide levels remained within target boundaries.
Based on standard utilization assumptions and at current fuel prices, economic performance was quantified and compared to pre-demonstration targets (system payback of less than one year for the demonstration boiler). It was calculated that for a 25 MMBtu/hr boiler fired by natural gas:
- The adoption of O2 trim would enable yearly savings exceeding 2400 MMBtu of gas, about 3%, or $13,500 cost savings. The further upgrade to CO/O2 trim technology would enable yearly savings exceeding 3000 MMBtu of gas, about 4%, or $17,000 cost savings.
- Payback for upgrading to O2 trim technology would be 2 years with a net present value (NPV) of $77,000 over 10 years. For the CO/O2 trim solution, 2.4 years payback and NPV of $88,000 was estimated.
- Every year, 144 tons of CO2 emissions would be avoided with O2 trim, 181.5 with CO/O2 trim technology.
During the demonstration, the controller performance was observed relative to ease of use, installation, and maintainability, and positive feedback relative to its deployment was collected.
When adopted for all 10 to 100 MMBtu/hr oil and natural gas boilers older than 10 years across the Department of Defense (DoD), the demonstrated technology has the potential to save $150 million in fuel costs annually and avoid the emission of approximately 769,000 tons of CO2.
Other findings impacting broad implementation include:
- Savings and economic indicators would be more favorable for larger boilers. Estimates for a natural gas-fired 100 MMBtu/hr boiler showed payback of 4 months and fuel cost savings of hundreds of thousands of dollars.
- Fuel-to-steam efficiency improvements of 7% to 8% were measured across the firing range when No. 2 oil was used as the fuel, but demonstration was limited to the O2 trim technology. Estimates for operation with oil are 7% ($140,000) fuel savings and payback of 0.2 years for a 25 MMBtu/hr boiler.
This project demonstrated that combustion control technology is a viable solution to achieve substantial fuel savings and reduced carbon footprint and easy to install for boiler retrofit, enabling quick return on investment. In particular, it has been shown how CO/O2 trim technology can lead to substantial energy savings. The new CO/O2 control solution was tested at its prototype stage (TRL6), and further development, testing, and certification is needed for product release (TRL8). This study will enable further engagement with key decision makers on installations and through energy service companies, leading to future potential adoption across DoD.
Points of Contact
Dr. Guido Poncia
United Technologies Research Center
Energy and Water
SERDP and ESTCP